1. Field of the Invention
The present invention relates to a method of determining a quasi-phase matching efficiency in a periodically poled structure of an optical waveguide, a periodically poled structure of an optical waveguide and an optical waveguide using the same, and more specifically to a periodically poled structure capable of maximizing a conversion efficiency in a non-linear optical phenomenon by determining an optimum length of electrodes for a quasi-phase matching.
2. Description of the Related Art
In the study of optical phenomena related to a non-linearity, one of the main concerns has been focused on the achievement of higher conversion efficiency in such phenomenological processes. Quasi-phase matching, which intentionally drives light waves to an interaction with a periodic structure of a nonlinear material, was introduced for the purpose (Phys. Rev., vol. 127, pp. 1918–1939, 1962, entitled “Interactions between light in a non-liner dielectric”, written by J. A. Armstrong, N. Bloembergen, J. Ducuing, and P. S. Pershan). The method of the quasi-phase matching by periodic poling was applied to such materials as lithium niobate, a silica fiber, and a polymer waveguide to obtain second harmonic generations successfully.
In a physical point of view, poling is to reconstruct or induce the second order nonlinear coefficient of the materials by means of an external electric field and the periodic poling is to impose an additional periodicity on the nonlinear coefficient. The exact origin of the non-linearity induction is not known yet but it is on the whole believed that the poled status and degree of the nonlinear materials are explicitly dependent on the applied electric field. In the periodic poling, a distribution of the external electric field as well as its intensity plays a crucial role in fitting the required quasi phase matching to improve the conversion efficiency.
In a conventional fabrication method of a quasi phase matching electrode in normal metal-contact poling, the electrode is as a rule designed to fit ½ of a quasi phase matching period, assuming that the region in contact with the electrode is under a constant field provided by the periodic electrode but the remaining half region in the period is in the absence of any field. In spite of such intension, the field leakage out of the periodic electrode region is unavoidable and undoubtedly believed to diminish the poling efficiency in a severe way. Therefore, a solution to this problem has been required.